US 20060201203 A1
The invention relates to a method for preparing a material exhibiting photocatalytic properties and comprising at least partially crystallised titanium oxide, in particular in the form of anatase at temperatures higher than 600° C. Said invention also relates to a glass sheet whose at least one face is coated with a material which contains titanium oxide and is thermally treatable at a temperature higher than 600° C. by such methods as quenching and/or bowing, but preserving the photocatalytic activity and required optical properties thereof for a clean-surface glazing. The invention also relates to a monolithic foliated glazing which is simple or multilayer and comprises said glass sheet, and to the use of said glazing for a building, a transport vehicle, as an ordinary glazing, for interior use, street furniture, mirror, a display system screen and photovolatic glazing.
1. A method of preparing a material exhibiting photocatalytic properties comprising a coating comprising at least partially crystallized titanium oxide, comprising
heating a transparent or semi-transparent substrate,
wherein the substrate comprises a coating of titanium dioxide on at least a first face of the substrate,
to a temperature greater than 600° C., and
conducting crystallization of the titanium dioxide at the temperature greater than 600° C.
thereby at least partially crystallizing the titanium dioxide and forming the material.
2. The method of
3. The method of
4. The method of
5. The method of
6. The method of
7. The method of
8. The method of
9. A glass sheet, at least one face of which comprises a coating of a material comprising titanium oxide, wherein the glass sheet is capable of undergoing a heat treatment at above 600° C. while still preserving the photocatalytic activity and the optical quality that are required for antisoiling glazing.
10. The glass sheet as claimed in
11. A laminated glazing, comprising the glass sheet of
12. A single or multiple, laminated, monolithic glazing, comprising the material exhibiting photocatalytic properties obtained in accordance with the method of
13. The glazing as claimed in
14. The glazing as claimed in
15. The application of glazing of
16. The method of
17. The method of
18. The method of
19. The method of
20. The method of
The present invention relates to glazing provided with a coating exhibiting photocatalytic properties, of the type comprising at least partially crystallized titanium oxide, especially in anatase form.
Several techniques are known for forming such a coating, especially on a glass sheet, with a view to obtaining a product of high optical quality. Available techniques include, for example, a sole-gel process, consisting in depositing a titanium dioxide precursor in solution followed by heating so as to form the dioxide crystallized in anatase form, a pyrolysis process, especially CVD (Chemical Vapor Deposition), in which titanium dioxide precursors in a vapor phase are brought into contact with the hot substrate, optionally during cooling, in particular the atmosphere face of a float output glass.
Cathode sputtering, known from patent WO 97/10186, proves also to be particularly advantageous from the standpoint of industrial scale-up. This is a vacuum technique that makes it possible, in particular, for the thicknesses and the stoichiometry of the deposited layers to be very finely adjusted. It is generally enhanced by a magnetic field for greater efficiency. It may be reactive sputtering, in which case it starts with an essentially metallic target, here based on titanium (optionally alloyed with another metal or with silicon), and the sputtering takes place in an oxidizing atmosphere, generally an Ar/O2 mixture. It may also be nonreactive sputtering, in which case it starts with a ceramic target already in the oxidized form of titanium (optionally alloyed). The titanium dioxide produced by cathode sputtering is generally amorphous and poorly crystallized, and it has to be heated subsequently for it to crystallize in the photocatalytically active form.
Application WO 02/24971 discloses the deposition on glass of partially crystallized anatase titanium dioxide by cathode sputtering at a relatively high working pressure of at least 2 Pa; in a first variant, during the deposition the substrate is for example at 220-250° C., a conventional annealing operation at about 400° C. then being carried out if required; in a second variant, the deposition is carried out on the substrate at room temperature, and then the coated substrate is heated to 550° C. at most, for a few hours.
In the current state of knowledge, if particular properties requiring an annealing, bending, toughening or other heat treatment at above 600° C., or even up to 700° C. in certain cases, are required for glazing coated with photocatalytic TiO2, the expert would inevitably deposit the TiO2 or its precursors after this heat treatment and would then activate or react the precursors by applying a more moderate temperature. In particular, it is considered that temperatures above 600° C. favor crystallization of TiO2 in the rutile form, which is photocatalytically less active than the anatase form.
Now, the inventors have succeeded in obtaining high photocatalytic activity and high optical quality by crystallizing the titanium dioxide at the temperatures of conventional glass heat treatments, thereby achieving this crystallization by the single toughening or other heat treatment and avoiding an additional subsequent heating operation at a more moderate temperature.
For this purpose, the subject of the invention is a method of preparing a material exhibiting photocatalytic properties comprising at least partially crystallized titanium oxide, especially in anatase form, characterized in that it employs temperatures in excess of 600° C. As a result, there is better integration of this method into various industrial processes, which are simplified by the elimination of a specific crystallization operation at a relatively low temperature. The duration of these processes is correspondingly shortened thereby. There are fewer devices required, since the heating means accomplish two functions simultaneously. Finally the cost of these processes is reduced.
According to preferred embodiments and/or embodiments that particularly prompted the invention:
So as to provide excellent results in the illustrative examples below, the method of the invention comprises the deposition of a titanium oxide coating on a first face of a first transparent or semitransparent substrate of the glass or glass-ceramic type which, optionally, has been provided beforehand with one or more functional multilayers and/or functional layers, the nature of which will be described in detail later.
According to other advantageous features of the method of the invention:
The subject of the invention is also a glass sheet, at least one face of which bears a coating of a material comprising titanium oxide, characterized in that it is capable of undergoing or has undergone a heat treatment at above 600° C., such as a toughening and/or bending operation, while still preserving the photocatalytic activity and the optical quality that are required for antisoiling glazing.
Firstly, the heat treatment at above 600° C. does not affect the product to such an extent that it makes it unsuitable for use as antisoiling glazing; it has even been observed, not without surprise, that the photo-catalytic activity is comparable, or even superior in certain cases, to that obtained after heat treatments according to the teaching of the abovementioned application WO 02/24971 (for example in annealing at 500° C. for one hour).
Nor is the use of temperatures above 600° C. incompatible with high optical quality, by which it is essentially meant that there are no defects visible to the eye: haze, spots or pitting, cracks. Advantageously, from an industrial standpoint, the mean colorimetric variation ΔE in reflection on the coating side induced by the heat treatment is at most 2.8, preferably at most 2.3; this expresses the fact that the colorimetric response in reflection of the end product is close to that of the coating product before heat treatment. AE is calculated by the equation:
Other subjects of the invention consist of:
According to other preferred features of this glazing:
Another subject of the invention is the application of this glazing as “self-cleaning”, especially antifogging, anticondensation and antisoiling glazing, especially architectural glazing of the double-glazing type, vehicle glazing of the windshield, rear window, side window and wing mirror type for automobiles, windows for trains, aircraft and ships, utilitarian glazing, such as aquarium glass, shop window glass and greenhouse glass, interior furnishings, urban furniture (bus shelters, billboards, etc.), mirrors, screens for display systems of the computer, television and telephone type, electrically controllable glazing, such as electrochromic glazing of the liquid-crystal or electroluminescent type, or photovoltaic glazing.
The invention is illustrated below by means of examples.
In this example, the transformation of amorphous TiO2 obtained by magnetron sputtering into its active form by, on the one hand, an industrial toughening operation and, on the other hand, an annealing operation for one hour at 500° C. are compared.
The photocatalytic activity after the two treatments was determined by means of the stearic acid photo-degradation/infrared transmission test or SAT for short, this test being described in application WO 00/75087.
A 60 nm thick layer of SiOC was deposited on three specimens of 4 mm-thick clear soda-lime silicate glass by chemical vapor deposition (CVD) as described in application WO 01/32578, and a 100 nm thick SiO2 layer was deposited on three other specimens by magnetron sputtering.
TiO2 coatings of varying thickness were deposited on the six specimens by magnetron sputtering at a working pressure of 26·10−3 mbar, and then the photocatalytic activity of the coatings was determined as indicated above after the two aforementioned heat treatments.
The results are given in Table I below.
Contrary to what was expected, not only does the industrial toughening operation not reduce the photocatalytic activity unacceptably, but the latter is at least comparable to that resulting from TiO2 activation treatments known in the prior art, as represented in particular by WO 02/24971 already mentioned. In fact, the activity is no longer weak after toughening only in Trial 4.
Consequently, the TiO2 prepared here could be toughened from the photocatalytic activity standpoint, even by employing standard thicknesses of sublayers acting as barriers to the diffusion of alkali metals from the glass.
The above trials 1, 3 and 5, and also trials 7 and 8 characterized by respective thicknesses of the photocatalytic coating obtained of 27 and 19 nm (with the same SiO2 barrier sublayer and the same TiO2 formation conditions as in trials 1, 3 and 5), involved the measurement of the mean colorimetric change ΔE in reflection on the coating side induced by the industrial toughening operation. The meaning of the various parameters in the (L,a*,b*) colorimetry system and the equation for calculating ΔE from ΔL, Δa* and Δb* are as described above.
The results are given in Table II below.
The relatively small mean colorimetric changes, or even in some cases ideally changes of less than 2, express a small color change in reflection on the photocatalytic coating side after all the coating has undergone an industrial toughening operation. This avoids the undesirable production of toughened products that undergo an excessively large colorimetric change as a result of the toughening operation. It becomes easier to predict, from before the toughening operation, what the final color will be.
This example relates to a double glazing unit consisting of two 4 mm thick glass sheets between which there is a 15 mm thick air cavity. In this example and the following ones, the face 2 of the double glazing unit, i.e. that face in contact with the air cavity of the glass sheet intended to be installed closest to the external atmosphere (and not that intended to be on the inside of a building), is coated with a thermal control multilayer deposited by magnetron sputtering. This process is particularly practical for depositing layers of the most varied type, by varying and precisely controlling the thicknesses thereof, on an industrial scale.
Here, this multilayer was a low-emissivity multilayer, that is to say one that reflects thermal infrared radiation (for wavelengths of the order of 10 μm) and capable of keeping heat inside a building for example.
The combination of the thermal control multilayer on face 2 with a multilayer that included a photocatalytic TiO2 layer and an SiO2 sublayer acting as barrier to the diffusion of alkali metals, deposited by magnetron sputtering on face 1, intended to be in contact with the external atmosphere, was studied from the optical standpoint.
Hereafter, X and Y denote, respectively, the low-emissivity multilayers differing from that of Example 2 of application EP 0 718 250 A2 only by changing the thickness of the layer (2) to 25 nm, and layer (2) to 19 nm and layer (3) to 29 nm, respectively.
The following four glazing compositions defined below only by the glass sheet on the outside, were tested:
In this example and in Examples 4-7 below, all the multilayers were subjected to an industrial toughening operation. The optical characteristics of the glazing were determined in transmission and in reflection on the “interior” side of the building (i.e. face 4 of the double glazing unit, of which only faces 1 and 2 were functionalized as indicated above), in reflection on the “exterior” side of the building (face 1: glass or TiO2) (the light transmission and light reflection TL and RL in percent, chromaticity coordinates a* and b* in transmission and in reflection on both faces of the glazing, as mentioned above). The results are given in the following tables.
Comparison between glazing 3a and glazing 3b indicates in what way the addition of the photocatalytic coating is liable to disturb the optical properties of the glazing: thus, a reduction in TL, a substantial increase in RL on both faces, and an increase in chromaticity in reflection on both faces of the glazing toward the blue-green (negative a* and b* values) are observed.
Compared with glazing 3b, in glazing 3c some of the lost TL is recovered and the two RL values again advantageously approach those of glazing 3a, as do its colorimetric values in reflection.
The methodology of Example 3 was adopted for the following glazing (the multilayers on face 2 reflect the solar radiation, corresponding to average wavelengths of the order of 1 μm). In this example, X and Y denote, respectively, the solar-protection multilayer sold by Saint-Gobain Glass France under the registered trade mark SGG Coollite ST®108 and the multilayer obtained by increasing the outermost layer thicknesses of the latter by 3.7, on the proximal side of the glass substrate, and by ⅔ on the distal side, respectively:
In this example and the following ones, the glazing units were composed of two 6 mm thick glass sheets between which there was a 12 mm thick air cavity.
The results are given in the three tables below.
Here, the TL is little affected by the addition of TiO2, which also provides a slight reduction in yellow in reflection on the TiO2 (4b)/glass (4a) exterior side.
The modification of the solar-protection multilayer (4d) results in an increase in TL and a substantial reduction in RL on the interior side, accompanied by a slight increase in yellow in reflection.
Example 4 was repeated, X and Y denoting here, respectively, the solar-protection multilayer sold by Saint-Gobain Glass France under the registered trade mark SGG Coollite ST®120 and the multilayer differing from the latter only by increasing the thickness of the proximal layer of the glass substrate by a factor of 2:
5d: idem 5b/6 mm glass/Y.
5c in relation to 5b shows, compared with 5a, a partial recovery of the lost TL and of the two RL values and, notably, a complete recovery of the color in reflection on both sides, even with a slightly better coloration neutrality.
In 5d, the recovered TL is increased, the reflection on the interior side is slightly higher (less good) whereas the reflection on the exterior side (TiO2) is reduced to an even lower (better) level than the RL of 5a on the exterior (glass) side.
The previous example was repeated for the following glazing units, in which X and Y denote, respectively the solar-protection multilayer sold by Saint-Gobain Glass France under the registered trade mark SGG Coollite ST®136 and the multilayer differing from the latter only by the thickness of the proximal and distal layers of the glass substrate increased by a factor of 1.7 and 0.774, respectively:
6d: the same photocatalytic multilayer as in 6b/6 mm glass/Y.
The comparison between 6a and 6b is characterized by an increase in RL on the exterior side of the glazing and, to a lesser extent, by an increase in chromaticity of the second relative to the first.
By optimizing the photocatalytic multilayer 6c, some of the lost TL is recovered and the RL on the exterior side is again substantially reduced, while recovering the color in reflection on the same face (with even a more neutral colorimetric response than 6a).
By modifying the solar-protection multilayer 6d, the RL on the exterior (TiO2) side is lowered to an even lower level than that of 6a on the glass side, and the yellow component in reflection on the interior side of the glazing is reduced relative to that of the other three glazing units.
The previous example was repeated with the following glazing units, in which X and Y denote, respectively, the solar-protection multilayer sold by Saint-Gobain Glass France under the registered trade mark SGG Coollite ST®150 and the multilayer differing from the latter only by the elimination of the proximal layer of the glass substrate and by increasing the thickness of the intermediate layer by a factor of 1.5 and the distal layer by a factor of 0.68:
7d: the same photocatalytic multilayer as in 7b/6 mm glass/Y.
These show in particular the near recovery of color in reflection on the exterior side of 7c in relation to that of 7a.
This example relates to what is called a “four seasons” multilayer, providing both solar-protection and low emissivity, sold by Saint-Gobain Glass France under the registered trade mark Planistar®. Unlike the thermal control multilayers of the previous examples, but similar to those of the following examples the latter is not subjected to the industrial toughening operation, which is therefore carried out, if required, before the multilayer is deposited, on the glass sheet optionally provided with its TiO2 coating and the barrier sublayer.
The following glazing was tested:
8c: 18 nm TiO2/68 nm SiO2/8 nm Si3N4/58 nm SiO2/6 mm glass/Planistar®.
Glazing 8c, compared with 8b, restores the color, in reflection on the interior side, of 8a and also, on the exterior side, where the reduction in RL compared with 8b is moreover slightly more significant.
The thermal control multilayer was a solar-protection multilayer sold by Saint-Gobain Glass France under the registered trade mark SKN®154. The following glazing was tested:
9c: 18 nm TiO2/68 nm SiO2/8 nm Si3N4/58 nm SiO2/6 mm glass/idem 9a.
Here it is particularly manifest, on the exterior side, that for 9c an RL intermediate of that of the other two coated glasses is obtained and also a blue component of the color in reflection that is almost the same level as in the absence of TiO2 (9a).
The multilayer SKN®165B, again sold by the Applicant, was tested, and more particularly the following glazing:
10c: 18 nm TiO2/69 nm SiO2/9 nm Si3N4/49 nm SiO2/6 mm glass/ . . . idem 10a.
A 50 nm thick SiOC layer acting as barrier to the migration of alkali metals and covered with a 15 nm thick photocatalytic TiO2 layer was formed by a CVD process on a glass sheet, reproducing Example 5 of patent EP 0 850 204 B1.
The photocatalytic activity, determined by photodegradation of stearic acid followed by infrared transmission, as previously, was 9·10−3 cm−1min−1 and, after industrial toughening, 7·10−3 cm−1min−1. This corresponds with the functionality being largely and satisfactorily retained.
The invention therefore makes it possible to produce glazing with antisoiling photocatalytic coatings that can be toughened and are of high activity, under the optimum industrial conditions, with light transmission and reflection levels and colorimetric characteristics in transmission and in reflection that can be readily adjusted to the values desired by the user.